Abstract
IAA, a major native auxin, has been shown to be involved in many physiological events. In gravitropic response, by using monocot coleoptiles, it has been postulated that re-distribution of IAA induces gravitropic bending. However, whether IAA molecule itself is necessity factor for gravitorpic bending or not is unclear. Our recent works based on immunolocalization of IAA efflux carrier PIN have revealed polar IAA transport in maize coleoptiles. In tip region of coleoptiles, PIN was localized in whole plasma membrane. In subapical region, polar staining patterns were observed. Gravity bending was completely suppressed by the local tip treatment of the transport inhibitors NPA. At this time, no differential distribution of IAA between upper and lower half was observed. The present results indicated that correct transport and distribution of IAA, by the regulation of ZmPIN1, in the coleoptiles after gravistimulus is absolutely necessary for gravitropic bending.
